1. Field of the Invention
The present invention relates to a lead frame, particularly, a lead frame capable of easily connecting an inner lead to an electrode of a semiconductor element by way of a bump of the inner lead; and a method of manufacturing the lead frame capable of easily forming the bump.
2. Description of the Related Art
Some lead frames have a structure that the inner end portion of the front surface of an outer lead made of copper is connected to the base end portion of the rear surface of an inner lead, by way of an intermediate layer made of aluminum which acts as an etching stopper in the etching for patterning the outer lead and the inner lead. In most of these lead frames, the leading edge portion of the inner lead has a bump made of aluminum, and is connected to an electrode pad of a semiconductor element by way of the bump.
The bump of the lead frame has been formed by a method wherein, for example, when the etching for patterning an inner lead and an outer lead is performed and thereafter an intermediate layer made of aluminum acting as an etching stopper in the above etching is etched using the inner lead and the outer lead as a mask, the portion where the bump is to be formed is also masked.
Such a lead frame, however, presents a problem in bonding of the leading edge of the inner lead to an electrode pad of a semiconductor element. When the position at which the leading edge of the inner lead is pressed by a bonding tool is slightly shifted from the bump position along the longitudinal direction of the inner lead, it becomes difficult to obtain good bonding.
Another problem occurs in a method of manufacturing such a lead frame. Namely, the formation of the bump additionally requires a series of photoresist selectively forming processes including the formation, exposure, development of a photoresist film, thus increasing the number of the processes.
Additionally, there occurs an inconvenience in shifting the forming position of the bump due to the deviation in the mask adjustment. The shifting of the forming position of the bump leads to the defective bonding.